tum, which, of course, is serially homologous with the mesonotum, is very narrow antero-posteriorly and separated from the mesonotum by a large, unpaired, semi-circular element, the scutellum. Between the scutellum and metanotum, a small piece, the metaparapteron, or postscutellum, is intercalated on each side. The hind-wing is inserted

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pn....

teg..

rpt

min

sct

enn

Sc

pet

FIG. 7. Dorsal aspect of

thorax of male Ponerine ant, Paraponera clavata. (Emery.) a' and a2, Anterior and posterior wings; pn, pronotum; sc, scutum of mesonotum; SM, Mayrian furrow; pss, parapsidal furrow; pps, parapsis; teg, tegula; ppt and ppt', paraptera of meso- and metathorax; sct, scutellum; mtn, metanotum; epn, epinotum; pet, petiole.

between this metaparapteron and the metepimeron. The epinotum, which, as we have seen, is morphologically the first abdominal segment, is large and convex and in many ants furnished with a pair of stout spines or teeth. It is closely applied to the metathorax from the posterior edge of the mesonotum above to the ventral edge of the metathorax below.

The thorax has on each side three openings, or stigmata, to the respiratory tubes, or tracheæ. The first, belonging morphologically to the mesothorax, lies beneath a small flap-like expansion of the pronotum where it abuts on the mesepimeron. The second or metathoracic stigmata lies beneath the insertion of the hind-wing and near the posterior end of the mesepimeron. The third stigma, belonging to the first abdominal segment, is distinctly seen on the side of the epinotum.

In the female ant (Fig. 8, A) the thorax is constructed on the same plan as that of the male, but is more robust and lacks the Mayrian furrow, which is also absent in the males of many genera. The males and females of most species, however, exhibit a greater simplification. of the pleural region of the thorax, owing to the fusion of the epimera and episterna with each other and often also with the sterna in the meso- and metathorax, and a very intimate fusion of the epinotum with the latter segment.

Turning to the workers, which are wingless, there is noticeable a great reduction in the size of the meso- and metathorax plus the epinotum, so that the three divisions of the thorax are more nearly of uniform size (Fig. 8, C, Fig. 9, a). In certain species, and especially in the ergatoid females (Fig. 8, B) and soldiers of a few genera, the various dorsal elements, such as the paraptera, scutellum and meta

notum may still be recognized as very small sclerites, but in the workers of the highest and most specialized ants of the genera Formica and Camponotus the thorax appears to consist of three similar segments,

FIG. 8. Thorax of female, ergatoid and worker Ponerine ants in profile. (Emery.) A, Myrmecia pyriformis, deälated female; B, M. spadicea, ergatoid female; C, M. pyriformis, worker; msn, mesonotum; the remaining letters the same as in Figs. 6 and 7.

owing to the disappearance of the scutellum, paraptera and metanotum as separate sclerites and to the fusion of the various elements in the pleural region of each segment.

The legs of the ant show much less variation in structure than the

FIG. 9. Median sagittal sections to show difference of development of thoracic segments in the worker and female Myrmica rubra. (Janet.) A, Worker; B, female; a, posterior portion of head; b, prothorax; c, mesothorax; d, metathorax; e, epinotum (first abdominal segment); f, petiole (second abdominal segment).

thorax and are, therefore, of less taxonomic value. Each of these appendages consists of the same fixed number of joints, the coxa, trochanter, femur, tibia, and five tarsal joints. The first tarsal joint, often

FIG. 10. Strigil of Texas harvester (Pogonomyrmex molefaciens. (Original.) a, Distal end of fore tibia; b, movable, pectinated spur; c, first tarsal (metatarsal) joint.

called the metatarsus, is much elongated, especially on the middle- and hind-legs, where it functions as a kind of secondary tibia, while the terminal tarsal joint bears a pair of usually simple, but sometimes. toothed, or pectinated claws. All of the tibiæ may be provided at their distal ends with spurs. These are always large and pectinated on the fore-legs, but may be simple on the middle and hind pairs. The finely and regularly pectinated spur of the fore tibia (Fig. 10, b) is of special interest on account of its beautiful structure and its function as a strigil. It is movable and curved and its concavity is opposite a similar concavity, fringed with bristles, on the base of the metatarsus. The ant draws its antennæ and posterior legs between the two opposed, pectinated surfaces and thus wipes off any adhering foreign matter.

The wings have not been used to as great an extent in descriptive works on ants as in those on other families of Hymenoptera, owing to their frequent absence in female specimens and to the permanently apterous condition of the workers, which have hitherto formed the basis of our systematic study. The venation of the fore wings, however, often exhibits important generic or even specific characters and its study, especially in fossil ants, is indispensable. It is sometimes highly variable in detail, even in males and females reared from

FIG. 11. Anterior wings of ants. (Original.) A, Ichnomyrmex cockerelli, female; B, Camponotus sansabeanus, female; C, Eciton schmitti, male; D, Strumigenys pergandei, female; E, Lasius claviger, female; F, Dolichoderus mariæ, female; G, Solenopsis molesta, female; H, Forelius maccooki, female; I, Myrmica scabrinodis, female; K, Pachycondyla harpax, male; L, Pogonomyrmex molefaciens, female; M, Tetramorium cespitum, female; N, Aphænogaster fulva, female; O, Trachymyrmex septentrionalis, female. The following are the veins of the wing: a, costal; b, subcostal; c, externomedian; d, anal; s, apterostigma; c, and g, cubital; h, discoidal and subdiscoidal; f, marginal, or radius; z, transverso-median; n, basal; m, recurrent; o, first section of radius in A, B, C, E and O, transverse cubitus in F, I and N. The following are the cells: u, first discoidal; v, costal; i, median, submedian; y. second discoidal; w, first cubital; w', second cubital. (These terms are used in myrmecography. Some authors, like Handlirsch, regard what is here called the "subcostal" as the radius + median, and the "subdiscoidal" as a branch of the median.)

the same mother. Several of the different types of venation which have been recognized are represented in the accompanying illustrations (Fig. II), to which the reader is referred for the names and disposition of the various veins and cells.

The Abdomen. This region in ants is very highly specialized in all three sexual phases. In some of the most primitive tribes, like the Amblyoponii and Cerapachysii, there is no sharp separation of the segments into a pedicel and gaster; the basal, though somewhat narrower and more accentuated, preserving essentially the same structure as the more distal segments. In most ants, however, there is a welldefined pedicel which may consist of either one or two segments, very movably articulated with each other and with the thorax and gaster. In the subfamilies Dolichoderinæ and Camponotinæ the pedicel always consists of but a single segment, the petiole, which is morphologically the second abdominal segment. The same condition prevails in most Ponerinæ, except that there is a constriction behind the following or third segment, foreshadowing the development of a postpetiole. This segment is clearly separated off in all Myrmicinæ, so that in the ants of this subfamily the pedicel consists of two highly specialized, nodiform segments, and the first gastric is the fourth instead of the third abdominal segment, as in the Camponotinæ, Dolichoderinæ and Ponerinæ. In the Doryline the genera Eciton and Enictus have a distinct petiole and postpetiole in the worker, but only a single segment, the petiole, in the male and female. In Dorylus and Cheliomyrmex the base of the abdomen of the worker is more primitive and more like that of certain Ponerine ants (Amblyopone and Cerapachys).

The base of the abdomen is the seat of an interesting soundproducing, or stidulatory, organ. Landois, in a book called "Thierstimmen," published in 1874, was the first to find this organ in a Ponerine ant ("Ponera quadridentata," probably Ectatomma quadridens). He believed that he had seen a similar structure in the Camponotine Lasius fuliginosus, and a few years later Lubbock (1877) figured what he took to be a stridulatory organ in L. flavus. Sharp (1893) and Janet (1893b, 1894b) have since carefully investigated these organs in several different ants. The former succeeded in finding them only in the Ponerinæ and Myrmicinæ (excepting the Cryptocerii) and believed them to be absent in the Dorylinæ, Dolichoderinæ and Camponotinæ. The organ (Fig. 12) is best described as a file made of extremely fine, transverse and parallel ridges on a small area in the mid-dorsal, chitinous integument at the very base of the first gastric segment, where it is covered by the overlapping portion of the preceding segment. The edge of this segment (Fig. 12, Bp) is sharp and